In the OSI (Open System Interconnection) standardization which is currently being promoted by the ISO (International Organization for Standardization), an OSI reference model is defined in which networks are hierarchically organized to verify the interconnectivity between the networks.
The internet, which has become widespread in recent years, is constructed by using the TCP/IP protocol, and this protocol corresponds to a network layer and a transport layer of the OSI reference model. Further, there is the IEEE 802.3 as one of the lower layers of the TCP/IP. This IEEE 802.3 corresponds to a data link layer of the OSI reference model.
In the network layer of the OSI reference model, in order to uniquely identify network devices in a network where a plurality of LANs are interconnected, a network layer address should be assigned to each network device. If the same network layer address is set on different network devices, communication at the network layers cannot be performed normally.
The network layer addresses may be managed by a network administrator, or the network layer address may be managed automatically. To be specific, in the former method, a network administrator manages a plurality of available network layer addresses and how the addresses are used, and performs address assignment when a network is established. In the latter method, a plurality of available network layer addresses are automatically assigned by using the DHCP (Dynamic Host Configuration Protocol, RFC2131), which is a kind of TCP/IP protocol.
On the other hand, also in the data link layer, in order to uniquely identify network devices in a LAN to which the network devices are connected, a data link layer address must be assigned to each network device. If the same data link layer address is set on different network devices in the same LAN, communication at the data link layers cannot be performed normally.
The data link layer addresses are managed as follows. A rule is determined among the manufacturers of network devices so that the same data link layer address is not assigned to different network devices, and the manufacturers assign data link layer addresses to the respective network devices according to this rule.
However, since a data link layer address set on a network device can be changed by the user, there is a possibility that the user may set a data link layer address which is already set on another network device. Further, since there is a limit to the number of data link layer addresses, when the number of network devices increases considerably, it is impossible to assign different data link layer addresses to the respective network devices. Further, since the communication by the network layer protocol depends on the data link layer protocol which is the lower-layer protocol, it is difficult to change the data link layer address by using the network layer protocol.
For the reasons described above, the address administrator must conventionally perform the work of changing the data link layer address directly to the target network device. There have been proposed two methods of setting data link layer addresses and network layer addresses, as follows. The first method is to set a data link layer address and a network layer address under the state where the network function is unavailable, and the second method is to assign a single network layer address to a specific data link layer address. Hereinafter, these methods will be briefly described with reference to the drawings.
Initially, the above-mentioned first method (first prior art), i.e., the method of setting a data link layer address under the network function unavailable state, will be described with reference to FIG. 5.
FIG. 5 is a block diagram illustrating an example of the construction of the first prior art. In FIG. 5, B500 denotes an apparatus for setting data link layer addresses, B501 denotes a data link layer address inputting means for inputting a data link layer address from a network administrator, and B502 denotes a data link layer address setting means for setting a designated data link layer address on a network device. A data link layer address inputted to the data link layer address inputting means B501 is supplied to the data link layer address setting means B502, and the data link layer address setting means B502 changes the data link layer address of the network device to the inputted data link layer address.
Next, the above-described second method (second prior art), i.e., the method of assigning a single network layer address to a specific data link layer address, will be described with reference to FIG. 6. In other words, this second method is to set a network layer address on a network device so that the same address is not set on another network terminal.
FIG. 6 is a block diagram illustrating an example of the construction of the second prior art.
In FIG. 6, B600 denotes an address management apparatus for managing network layer addresses; B601 denotes a network layer address storage means for storing the correspondence between network layer addresses and data link layer addresses in a network layer address table; B602 denotes a network layer address search means for searching the network layer address table for an unused network layer address which is not associated with a data link layer address; B603 denotes a network layer address updation means for updating the correspondence between a data link layer address and a designated network layer address; B604 denotes a network layer address assignment instruction means for transmitting a network layer address assignment instruction which instructs an assignment of a network layer address; B605 denotes a network layer address assignment instruction detection means for detecting a network layer address assignment instruction which instructs an assignment of a network layer address; B606 denotes a network layer address setting means for setting the inputted network layer address on a network device; B607 denotes a network layer address assignment request means for transmitting a network layer address assignment request which requests for an assignment of a network layer address; B608 denotes a network layer address assignment request detection means for detecting a network layer address assignment request; and B609 denotes a corresponding data link layer address search means for searching the network layer address table for a network layer address corresponding to a designated data link layer address.
FIG. 15(A) shows the construction of a network layer address assignment request D1500.
The network layer address assignment request D1500 is composed of a destination data link layer address field D1001 as an area where a destination data link layer address is stored, and a source data link layer address field D1002 as an area where a source data link layer address is stored.
FIG. 15(B) shows the construction of a network layer address table D1503.
The network layer address table D1503 contains a plurality of network layer address correspondence lists D1504, and each list D1504 is composed of a data link layer address field D1505 where a data link layer address is stored, and a network layer address field D1506 where a network layer address corresponding to the data link layer address is stored.
FIG. 15(C) shows the construction of a network layer address assignment instruction D1507.
The network layer address assignment instruction D1507 is composed of a destination data link layer address field D1001 where a destination data link layer address is stored, a source data link layer address field D1002 where a source data link layer address is stored, a destination network layer address field D1003 where a destination network layer address is stored, a source network layer address field D1104 where a source network layer address is stored, and an assignment network layer address field D1508 where a network layer address to be assigned is stored.
FIG. 21 is a flowchart for explaining the operation of the whole address management apparatus according to the second prior art.
The network layer address assignment request means B607 sets the data link layer address of the self network device in the source data link layer address field D1002 of the network layer address assignment request D1500, sets a data link layer broadcast address, in the destination data link layer address field D1001, indicating all of other network devices to be connected to a LAN to which the self network device is connected, and then transmits the network layer address assignment request D1500 (S2100).
The network layer address assignment request detection means B608 performs detection of a network layer address assignment request (S2101). When any of the network devices in the LAN, each having a network layer address assignment request detection means, detects the network layer address assignment request D1500, the detecting network device extracts the data link layer address from the source data link layer address field D1002 in the network layer address assignment request D1500, and sets the data link layer address in the destination data link layer address field D1001 in the network layer address assignment instruction D1507 (S2102).
When the corresponding data link layer address search means B609 detects, from the network layer address table D1503, a network layer address corresponding to the source data link layer address in the network layer address assignment request D1500 (S2103, S2104), the corresponding data link layer address search means B609 sets this address in the assignment network layer address field D1508 (S2110).
The network layer address search means B602 searches the network layer address table for an unused network layer address (S2105). When there is no unused network layer address, the network layer address search means B602 ends the process. When an unused network layer address is detected (S2106), the network layer address assignment instruction means B604 sets the unused network layer address in the assignment network layer address field D1508 in the network layer address assignment instruction D1507 (S2107).
Then, the network layer address assignment instruction means B604 sets the data link address in the source data link layer address field D1002 in the network layer address assignment instruction D1507, sets the network address in the source network address field D1004 in the network layer address assignment instruction D1507, and transmits the network layer address assignment instruction D1507.
The network layer address assignment instruction detection means B605 detects the network layer address assignment instruction D1507, and the network layer address setting means B606 extracts the assignment network layer address field D1508 from the network layer address assignment instruction D1507 and sets the network layer address in the field D1508 (S2108). The network layer address updation means B603 enters the correspondence between the data link layer address to which the network layer address assignment instruction is directed and the network layer address which has instructed assignment into the network layer address table D1503 in the network layer address storage means B601 (B2109).
In the above-described first prior art, however, since there is no means for obtaining the data from the network, it is impossible to set the data link layer address through the network. That is, in this first prior art method, the network must be temporarily halted to set the data link layer address.
Furthermore, according to the second prior art, since the data link layer address is used to decide the destination of the network layer address assignment instruction, even if the same data link layer address is set on plural network devices, it is impossible to distinguish these devices from each other on which the same data link layer address is set. That is, there is the possibility that the same network layer address might be set on plural network devices.